Generally, marine engines, etc., are air-cooled engines, in which there is adopted a system to draw up water by pump and discharge the water after the water has been circulated within the engine. When the engine is overheated because of an occurrence of something abnormal to the cooling water in conventional systems, a temperature sensor attached to a cylinder head or in the neighborhood thereof outputs a signal when it detects a preset temperature and activates an audible buzzer, and furthermore activates the regulation of engine speed or the like.
On the other hand, when attention is paid to the abnormality of cooling water, there is a conventional system wherein a pressure sensor or a cooling water detecting sensor is attached likewise to the cylinder head or a water channel in the neighborhood thereof in order to detect the fact that the cooling water flow has stopped or is reduced and to warn the operator of the abnormality of cooling water (in the case of a cooling water) by buzzing a buzzer and regulating the engine speed.
The most troublesome problem inherent in the system having the temperature sensor attached to the cylinder head or the neighborhood thereof is determining what the preset temperature should be. Since the detected temperature is a temperature increasing owing to abnormality of the engine, if the preset temperature is too high, the alarm is too late. On the contrary, if the preset temperature is too low, the alarm is issued even within a normal temperature range. Therefore, experiments to determine this preset temperature are very troublesome. Furthermore, careful attention must also be paid to irregularity of sensors and heat conduction.
An object of the present invention is, in view of the above-mentioned inconveniences inherent in the prior art, to provide an overheat detecting apparatus for an engine which is capable of rapidly detecting an occurrence of an overheated state of an engine particularly by catching the rate of abrupt temperature increase occurable at one stage of engine overheating and effectively preventing the same.
The present invention includes a temperature sensor attached to a cylinder head or the neighborhood thereof, alarm means for issuing an alarm to the outside when said temperature sensor detects an overheating state of the engine, and a main control unit for inputting an output signal from said temperature sensor and actuating said alarm means to indicate that it is necessary to regulate the engine speed.
The main control unit includes a temperature increase rate calculating function for calculating a temperature increase rate of the engine in accordance with an output signal from said temperature sensor, and an alarm control function for actuating said alarm means and regulating the engine speed if such calculated temperature increase rate of the engine becomes a predetermined value or more when the engine speed and engine temperature are within respective predetermined ranges of engine speed and engine temperature.
Recent marine engines, especially engines of outboard motors, employ a starting spark advance method for automatically advancing the ignition timing from the maximum spark delaying time in order to enhance the starting performance. This method employs not only such a function as to spark advance the ignition timing under a certain condition but also such a function for controlling the spark advance time or ignition timing by engine temperature. On the other hand, such engines generally include an overheat warning function for detecting, in the case engine is overheated due to inferior cooling water pumping or the like, rising engine temperature and giving a warning to the operator by generating a buzzer sound, lighting a lamp or the like.
A general spark advance mechanism for outboard motors is constructed such that a stator of a magneto is cooperatively worked with the opening degree of a throttle so as to be mechanically slided. However, there has been employed recently another method in which a throttle sensor is mounted on a throttle shaft of a carburetor, and signals of the opening degree of this sensor are input into an ignition circuit to obtain an ignition timing in correspondence with the opening degree of the throttle.
Furthermore, since a very low speed and smooth rotation called "trolling rotation" is required for the outboard motor, the ignition timing of the totally closed time of the throttle, in many cases, is considerably delayed from the top dead center for the purpose of lowering the exploding pressure. However, since the combustion speed is slow at the staring time, if the ignition timing is left as delayed, the starting performance is inefficient and it is necessary to spark advance close to 10.degree. before the upper dead center piston position.
In view of the above, the engines of the throttle sensor spark advance type employ, in many cases, such a function as to automatically spark advance at the starting time. In these engines, the duration of spark advance time is changed by a temperature sensor signal from a temperature sensor mounted in the vicinity of the cylinder head, or the ignition timing is steppingly changed.
On the other hand, the above-mentioned overheat warning temperature sensor is separately exclusively employed and likewise mounted in the vicinity of the cylinder head.
However, in the above-mentioned conventional systems, the starting spark advance controlling temperature sensor and the overheat warning temperature sensor are, as a matter of course, independent and separate from each other so as to be independently separately employed. For this reason, the layout of mounting these sensors becomes complicated. Furthermore, since the installing places of these sensors are different, the associated coefficient of thermal conductivity is also different and the test for setting a working temperature is troublesome. Moreover, since two sensors are required, the cost becomes high. In addition, since signals are to be input into two sensor systems, the circuit construction becomes complicated and the cost becomes high.
Another object of the present invention is to provide an engine ignition timing control apparatus which is capable of obviating the inconveniences of the prior art, simplifying the overall construction especially by concentrating the construction of the temperature sensor circuit into one system, and lowering the cost of the overall apparatus without lowering the efficiency.
An engine ignition timing control apparatus of the present invention includes a temperature sensor disposed on or in the vicinity of a cylinder head, warning means for issuing a warning to the outside when the temperature sensor detects an overheating state of the engine, and a main control portion for inputting output signals from the temperature sensor, regulating the increase of engine speed, and driving said warning means in accordance with necessity. The main control portion further includes a starting time ignition timing control function for normally inputting output signals from the temperature sensor and controlling the spark advancement at the starting time of the engine on the basis of engine temperature information transmitted from said temperature sensor.